Am 30. Juli 2020 22:11:39 MESZ schrieb Heinrich Schuchardt xypron.glpk@gmx.de:
Am 30. Juli 2020 20:31:47 MESZ schrieb Atish Patra atishp@atishpatra.org:
On Thu, Jul 30, 2020 at 4:04 AM Heinrich Schuchardt xypron.glpk@gmx.de wrote:
On 30.07.20 12:16, Sean Anderson wrote:
On 7/30/20 6:03 AM, Heinrich Schuchardt wrote:
Dear Sean,
when trying to run grubriscv64.efi from the trini/u-boot-gitlab-ci-runner:bionic-20200526-18Jun2020 Docker
image on
a MAIXDUINO the relocations are not naturally aligned:
lib/efi_loader/efi_image_loader.c(133) efi_loader_relocate():
efi_reloc 000000008030a000, offset 0x101e, type 10Here we are trying to change an u64 at 0x8030B01E:
uint64_t *x64 = efi_reloc + offset; *x64 += (uint64_t)delta;This leads to an exception in function efi_loader_relocate():
Unhandled exception: Load address misaligned EPC: 00000000805a95ac RA: 00000000805a953a TVAL:000000008030b01e
EPC: 000000008001c5ac RA: 000000008001c53a relocThe GRUB image is available here:
https://gist.github.com/xypron/522a91962248e9c3888d8554cb61ad2c/raw/b9596616...
On QEMU the GRUB image is executed without problems:
https://gitlab.denx.de/u-boot/custodians/u-boot-efi/-/jobs/132919
The UEFI specification requires for the ARM platform that
unaligned
support is enabled. This is why we have implemented function allow_unaligned().
On RISC-V we have not yet implemented allow_unaligned() yet. Is
there a
way to switch RISCV64 CPUs especially the Kendryte K210 into a
mode
supporting unaligned access?
AFAIK RISC-V has no requirement that un-aligned loads/stores
complete. I
believe the recommended solution is to install a trap handler
which
completes the un-aligned load through a series of aligned loads
and
then
returns back to the application. For an example of such an implementation, check out arch/riscv/kernel/traps_misaligned.c in
Linux.
This may be too complex for U-Boot, so perhaps you can simply
disallow
unaligned accesses?
--Sean
Working around the problem inside U-Boot is easy (just some memcpy() calls) but the GRUB image itself also makes unaligned accesses:
Unhandled exception: Load address misaligned EPC: 000000008030b004 RA: 00000000805a4eca TVAL: 000000008030b02e EPC: 000000007fd7e004 RA: 0000000080017eca reloc
UEFI image [0x000000008030a000:0x0000000080433fff] pc=0x1004
This is what I found in "RISC-V Unprivileged ISA V20191213"
"Loads and stores where the effective address is not
naturally
aligned to the referenced datatype (i.e., on a four-byte boundary
for
32-bit accesses, and a two-byte boundary for 16-bit accesses) have behavior dependent on the EEI. An EEI may guarantee that misaligned loads and stores are fully supported, and so the software running
inside
the execution environment will never experience a contained or fatal address-misaligned trap."
@Leif Should GRUB be built with -mstrict-align for RISC-V?
That shouldn't be necessary. Any real board with an MMU that can boot Linux needs a SBI provider such as OpenSBI. OpenSBI already implements a
misaligned
handler.
Are we planning to support EFI booting for NoMMU platforms ? As per my understanding runtime services need to be mapped through kernel page tables.
My interest is to have an affordable hardware platform where I can test U-Boot's UEFI sub-system on RISC-V.
With 6 MiB usable RAM. (2 MiB reserved for AI) we probably won't get further than running GRUB.
Can OpenSBI be built for the Kendryte K210 SoC? What is the size of OpenSBI?
Yes: https://github.com/riscv/opensbi/tree/master/platform/kendryte/k210
So we should try if we can run U-Boot with OpenSBI on the platform.
Best regards
Heinrich
@Ard How about the EFI part of the Linux kernel?
Best regards
Heinrich